Conventionally, content such as a dictionary is made up of a single file described by 16-bit code character data in accordance with JIS-X4081. This dictionary content may be encrypted and retrieved as recited in International Publication Pamphlet No. 2006/123448, for example.
International Publication Pamphlet No. 2006/123448 recites that the retrieval may be performed with the dictionary content in a compressed state by using an appearance map configured by a bit string indicating, for each of character data, the presence/absence of character data in a file to be searched. This appearance map is data for performing a full-text search of a dictionary or knowledge in a mobile terminal such as a cellular phone and is data belonging to a zero-memory source and having an appearance ratio of 8% and random characteristics for “ON” of each bit.
Data compression of a zero-memory source is explained by Uematsu, Tomohiko, “Introduction to Document Data Compression Algorithm” (3.4 Encoding Based on Blocks and Effect Thereof (pp. 51 to 53)), CQ Publishing Company Ltd., Oct. 15, 1994. Uematsu, “Introduction to Document Data Compression Algorithm” (3.4 Encoding Based on Blocks and Effect Thereof (pp. 51 to 53)), CQ Publishing Company Ltd.; Oct. 15, 1994 explains the data compression of a zero-memory source taking an example of block encoding for every two bits and three bits, and when block length is increased, the compression rate is raised and an ideal compression may be implemented by approaching to information entropy.
However, if block length is increased with respect to the disclosure in International Publication Pamphlet No. 2006/123448, the amount of calculations for generating a Huffman tree exponentially increase. Therefore, if the disclosure of International Publication Pamphlet No. 2006/123448 is directly applied, a problem arises in that compression and decompression is not possible in a resource-saving environment such as a slow PC, a small memory, or a small disk space when a full-text search of a dictionary or knowledge is performed in a mobile terminal such as a cellular phone.